JP2944466B2 - Separation and recovery method of heavy metals from incineration ash - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for separating and recovering heavy metals from incinerated ash.
Alternatively, copper-containing compounds (sulfides) with a purity that allows heavy metals such as copper, lead, and zinc to be used as nonferrous smelting raw materials from incinerated ash from industrial waste, and heavy metal-containing compounds (sulfides) such as lead sulfide and zinc sulfide More particularly, the present invention relates to a method for separating and recovering heavy metals from incinerated ash which is suitable for separating and recovering heavy metals from incinerated ash containing various types and amounts of heavy metals.

[0002]

2. Description of the Related Art When municipal waste and industrial waste are incinerated,
Bottom ash (residue) and fly ash (fly ash) containing harmful heavy metals such as lead, zinc, cadmium and copper are generated. The former residue is landfilled as it is or after solidifying cement. Fly ash is designated as specially managed municipal waste due to its high content of harmful heavy metals.
Since it is mandatory to decontaminate by the waste cleaning method, after solidification, chelation solidification, and melt solidification, some of them are effectively used, but most of them are still fully satisfactory. It cannot be a processing technology.

[0003] Recently, it has become difficult to secure landfill sites, and a technique has been developed for melting slag by melting residues and fly ash in order to reduce incineration ash (residue and fly ash). . According to this technique, heavy metals are fixed in the slagified solid, but fly ash called volatile ash is generated when the incinerated ash is melted into slag, and the volatile ash contains heavy metals having a low boiling point (lead). , Zinc, cadmium, copper, etc.) are concentrated and contained in large amounts. In addition, a method has been developed in which fly ash is granulated into pellets and then fired at a high temperature to fix heavy metals and to be used as aggregate, etc. The ash contains concentrated heavy metals. As described above, each technique has a problem that a heavy metal cannot be recovered and treated.

[0004] As a method for recovering heavy metals from such incinerated ash, JP-A-49-113703, JP-A-53-25081, JP-A-58-46353, JP-B-58-53594, and JP-B-60 7948
And JP-A-4-265189. In these methods, a heavy metal dissolved in incineration ash is eluted to obtain a heavy metal dissolving solution, and a sulfide or hydroxide of the heavy metal is obtained by adding an alkali source such as sodium sulfide or sodium hydroxide to the solution. However, there is still insufficient technology for detoxifying harmful heavy metals in incinerated ash to recover valuable heavy metals and use them effectively. Because the heavy metal sulfides or hydroxides are precipitated and separated from the heavy metal solution at once and separated, the content of valuable heavy metals in the resulting sulfides or hydroxides is low, Since it does not satisfy the grade of purity required for raw materials (for example, copper content: 30 wt% or more, lead content: 40 wt% or more, zinc content: 50 wt% or more), heavy metals cannot be recycled This is because it must be discarded after being treated in some way.

As an improvement of such a method, there is a method described in JP-A-6-170354. This method aims to recover heavy metals from fly ash as non-ferrous refining raw materials by adding (dissolving) fly ash to a hydrochloric acid aqueous solution having a pH of 3 or less to elute heavy metals other than lead at a pH of 3 or less. Then, the filtrate is neutralized to pH 7 or more to precipitate and separate a hydroxide of a heavy metal mainly composed of zinc. However, since some of the lead compounds (mainly lead chloride) in fly ash are soluble in water and hydrochloric acid, it is practically difficult to separate lead to the residue side at a pH of 3 or less with high purity. is there. For example, two kinds of municipal waste incineration ash (ash I and ash II) obtained by the present inventors were dissolved in 100 g of a hydrochloric acid aqueous solution in an amount of 20 g to conduct a dissolution experiment, and the relationship between the pH of the solution and the dissolved lead concentration was determined. The results are shown in FIG. 1, and from this FIG.
It can be understood that the solubility of lead contained in the molten fly ash shows various values depending on the form of the compound and the correlation with coexisting substances. In the case of Ash I, about 1000 mg / l of lead already eluted at around pH 3. This amount of elution is about the same as the amount of lead in the ash used in the experiment.
This is equivalent to 50%, so that when collectively treating various fly ash, only lead cannot be fractionated and separated to the residue side with high purity.

Accordingly, as a further improved method, an acid is added to the incineration ash to elute all heavy metals including lead, and then the lead is precipitated and separated as sulfide at a pH of 0.4 to 1.2, and then the pH is reduced to a pH of 2. As described above, a method for precipitation and separation of heavy metal mainly composed of zinc as sulfide has been developed (Japanese Patent Application No. 6-178289).
issue). This method is a method for separating and recovering lead and zinc from incinerated ash, and can separate and recover lead and zinc as sulfides with high purity, which is more reliable and superior to the method described in JP-A-6-170354. It is a separate collection method.

[0007]

According to the method for separating and recovering lead and zinc from incinerated ash, the types and amounts of heavy metals in incinerated ash to be separated and collected, such as incinerated ash coming from a specific incineration plant, are compared. When the target is constant, it can be suitably used. However, when the types and amounts of heavy metals in the incineration ash to be separated and collected differ from day to day as in the case of treating incineration ash from incineration plants over a wide area at once (wide-area treatment), heavy metals are sulfided. In some cases, the amount of a precipitant such as sodium sulfide added for precipitating as a substance is not appropriate, and in that case, the following problem occurs. That is, when the amount of the precipitating agent is too small, the recovery rate of heavy metals for the purpose of separation, separation and recovery is reduced, and when the amount of the precipitating agent is excessive, the recovery rate is high, but the precipitation by the precipitating agent is not desired. , And the purity of the heavy metal for the purpose of separation and recovery is reduced. Further, when the amount of the precipitating agent is excessive,
Effluent from the separate collection process (hereinafter referred to as treated effluent)
The unreacted sulfur component therein increases, which raises COD (Chemical Oxygen Demand) and becomes a source of environmental pollution, and also causes a problem of reduced economic efficiency.

[0008] The present invention has been made in view of such circumstances, and its purpose is to vary the types and amounts of heavy metals in the incineration ash to be separated and collected, as in the case of wide-area treatment. Even in the case of different types of incineration ash from specific incineration plants, it does not cause a decrease in the recovery rate of heavy metals for the purpose of separation, separation and recovery, a decrease in purity, and an increase in the sulfur content in the treated wastewater. In the same manner as when the types and amounts of heavy metals in the incineration ash to be separated and collected are constant, the heavy metals for the purpose of separation and separation and collection can be separated and collected as sulfides with high purity and a high recovery rate. It is an object of the present invention to provide a method for separating and recovering heavy metals from incinerated ash, which can reduce the sulfur component content of ash.

[0009]

In order to achieve the above object, a method for separating and recovering heavy metals from incinerated ash according to the present invention comprises a method for separating and recovering heavy metals from incinerated ash having the following configuration (first method). To 6 inventions). That is, the first invention is the method according to claim 1, which comprises a heavy metal dissolving step of eluting heavy metals in the incineration ash in a heavy metal dissolving tank to obtain a heavy metal dissolving solution, and a first separating and collecting tank for the solution. Sent to
In this tank, sodium sulfide or sodium hydrosulfide is supplied to the solution, and the pH of the solution is adjusted, whereby a part of heavy metals in the solution is precipitated and separated as sulfide, and a first fractionation and recovery step is performed. The solution after the separation of the precipitate is fed to a second separation / recovery tank, and sodium sulfide or sodium hydrosulfide is supplied to the solution in this tank, and the pH of the solution is adjusted.
A second fractionation and recovery step of precipitating and separating some or all of the heavy metals in the solution as sulfides, the method comprising the steps of: Determined by quantitative analysis for each type of
The amounts of heavy metals precipitated in the first fractional recovery step and the amounts of heavy metals precipitated in the second fractional recovery step are calculated from the analytical values, and sodium sulfide or sodium hydrosulfide supplied in the first fractional recovery step is calculated. Is set as a sulfur amount on the basis of an amount chemically equivalent to the calculated amount of heavy metal precipitated in the first fractional recovery step, and sodium sulfide or sodium hydrosulfide supplied in the second fractional recovery step. Wherein the amount of sulfur is set as the amount of sulfur on the basis of a chemically equivalent amount to the amount of heavy metal precipitated in the second fractionation and recovery step calculated above, as a reference. .

A second aspect of the present invention is the method according to the second aspect, wherein a part of heavy metals in the solution is precipitated and separated as sulfide in the second separation and recovery step, and then the solution after the separation of the precipitate is separated. By feeding the solution to the third fractionation and recovery tank, and supplying sodium sulfide or sodium hydrosulfide to the solution in this tank and adjusting the pH of the solution, some or all of the heavy metals in the solution are converted into sulfides. A third separation and recovery step of precipitating and separating, wherein the amount of sodium sulfide or sodium hydrosulfide supplied in the third separation and recovery step is defined as a sulfur amount in the third separation and recovery step which is calculated from the analytical value. The method according to claim 1, wherein the amount is set based on a chemically equivalent amount to the amount of heavy metal to be made. A third invention is a method according to claim 3, a fourth invention is a method according to claim 4, a fifth invention is a method according to claim 5, and a sixth invention is a method according to claim 6.

[0011]

The method for separating and recovering heavy metals from incinerated ash according to the present invention comprises the steps of dissolving the heavy metals as described above, the first separating and collecting step,
A method for separating and recovering heavy metals from incineration ash having a second separation and recovery step, wherein the heavy metal content in the heavy metal dissolving solution obtained in the heavy metal dissolving step is determined by quantitative analysis for each type of heavy metal, and from the analysis value The amount of heavy metal precipitated in the first separation and recovery step and the amount of heavy metal precipitated in the second separation and recovery step are calculated in advance, and the amount of sodium sulfide or sodium hydrosulfide supplied in the first separation and recovery step is calculated as follows. The amount of sulfur is set on the basis of an amount that is chemically equivalent to the calculated amount of heavy metal precipitated in the first fractional recovery step,
The amount of sodium sulfide or sodium hydrosulfide to be supplied in the separation and recovery step is set as the sulfur amount based on an amount chemically equivalent to the calculated amount of heavy metal precipitated in the second separation and recovery step. .

Therefore, the first separation and recovery step and the second
The supply amount of sodium sulfide or sodium hydrosulfide in the separation and recovery step can be controlled to an appropriate amount without excess or deficiency. That is, it is possible to supply an appropriate amount of sodium sulfide or sodium hydrosulfide according to the amount of heavy metal to be precipitated as a sulfide in each of the first separation and recovery step and the second separation and recovery step. Alternatively, it is possible to prevent the amount of sodium hydrosulfide added from becoming too small or too large.

Therefore, as in the case of wide-area treatment, the type and amount of heavy metals in the incineration ash to be separated and collected vary widely from day to day, and the types and contents of heavy metals in the heavy metal dissolving solution obtained in the heavy metal dissolving step vary. Even if you do,
Incineration ash that is subject to separation and recovery, such as incineration ash from a specific incineration plant, without causing a reduction in the recovery rate of heavy metals, a reduction in purity, and an increase in the sulfur content in the treated wastewater for the purpose of separation, separation and recovery As in the case where the type and amount of heavy metals in the water are constant, the heavy metals for separation, separation and recovery can be separated and recovered at high purity and high recovery rate as sulfides, and the sulfur component content in the treated wastewater can be reduced. I can do it.

In the second separation and recovery step, when not all but part of the heavy metals in the solution are precipitated and separated as sulfides, the heavy metals can be further separated and recovered from the solution after the separation of the precipitates. The separation and recovery of such heavy metals is carried out by feeding the solution after separation of the precipitate to a third separation and recovery tank, supplying sodium sulfide or sodium hydrosulfide to the solution in this tank, and adjusting the pH of the solution. It can be carried out by performing a third fractional recovery step of precipitating and separating some or all of the heavy metals in the solution as sulfides.
At this time, the amount of heavy metal precipitated in the third separation and recovery step is calculated from the analysis value of the heavy metal content, and the amount of sodium sulfide or sodium hydrosulfide supplied in the third separation and recovery step is defined as the sulfur amount. It is preferable that the calculated amount of the heavy metal is set based on a chemically equivalent amount (the method according to claim 2). In this way, the supply amount of sodium sulfide or sodium hydrosulfide in the third separation and recovery step can be controlled to an appropriate amount without excess or deficiency. Even if the types and amounts of heavy metals in the materials vary from day to day, the heavy metals for the purpose of separation, separation and recovery can always be separated and collected as sulfides with high purity and a high recovery rate, and the sulfur component in the treated wastewater The amount can be reduced.

The pH of the solution can be adjusted by adding an alkali or an acid to the solution, and the pH of the solution can be checked by measuring the pH with a pH meter. the method of).

[0016]

FIG. 2 shows a process flow according to an embodiment.
The description will be made with reference to FIG. The incinerated ash carried in from various places is supplied to heavy metal dissolving tanks (A, B, C) and dissolved to obtain a heavy metal dissolving solution. At this time, the residue slightly remaining is often recovered and subjected to the melting treatment again. Next, these heavy metal dissolving solutions are analyzed within a few minutes by a liquid element amount measurement device represented by ICP (high frequency plasma emission spectrometer), quantified for each heavy metal element, and the analytical value is obtained. The amount of heavy metal precipitated in each separation and recovery step (each separation and recovery tank) is calculated.

Next, the supernatant of the heavy metal dissolving solution is
It is sent to a separation and recovery tank, and it is confirmed that the pH is appropriate for precipitation and separation of heavy metals (eg, Cu) to be separated and recovered in this tank (if the pH is not appropriate, adjust the pH by adding caustic soda or hydrochloric acid). Then, the amount of sodium sulfide or sodium hydrosulfide that is chemically equivalent to the amount of sulfur added to the amount of the heavy metal added with another coexisting heavy metal that precipitates as a sulfide at the pH is applied to the CPU (central processing unit = operation unit + control unit). Device). Then, the obtained amount or a slightly larger amount of sodium sulfide or sodium hydrosulfide is added to the solution in the above-mentioned tank, and after stirring for a certain period of time, the coagulated and precipitated sulfides (eg, CuS and other sulfides) are added to the lower part of the tank. And separate it. Then, this is dehydrated and washed to make a nonferrous smelting raw material (for example, a copper raw material).

Next, the solution after the separation of the sulfide precipitate (first
The supernatant of the separation / recovery tank is fed to a second separation / recovery tank, and the pH is adjusted to a suitable level for precipitation and separation of heavy metals (eg, Pb and Zn) separated and recovered in this tank. The amount of sodium sulfide or sodium hydrosulfide which is chemically equivalent to the total amount of precipitated heavy metals as sulfur is calculated by the CPU. Then, the obtained amount or a slightly larger amount of sodium sulfide or sodium hydrosulfide is added to the solution in the above-described tank, and the mixture is stirred for a certain period of time, and then the aggregated and precipitated sulfide (for example, PbS and ZnS and C
dS, etc.) from the bottom of the tank and separate. And
This is dehydrated and washed to form a nonferrous smelting raw material (for example, a lead or zinc raw material).

The solution obtained after the separation of the sulfide precipitate (supernatant of the second fractionation and recovery tank) is neutralized in a pH adjustment tank, and if necessary, desalted and discharged. Although a small amount of hydroxide precipitates during the neutralization, this precipitate contains almost no heavy metal, and is transferred to the slag side even after re-melting in a melting furnace, so that the precipitate is melt-processed. In addition, when impurities as a nonferrous smelting raw material are small, it is possible to raise the pH to 6 to 7 when precipitating and separating sulfide in the second fractionation recovery tank, and to carry out neutralization treatment simultaneously with heavy metal recovery. It is.

Analysis of the main components of the separated and recovered materials (precipitated and separated sulfides) when two kinds of municipal waste incineration ash (referred to as ash I and ash II) are subjected to the separation and recovery processing of heavy metals by such a process. The values are shown in Table 1. About Ash I
Since it contained a lot of Cu, it was recovered as a Cu raw material and a Pb + Zn raw material. As a result, 52.9% as a Cu raw material and 58.4% (17.1% + 41.3%) as a Pb + Zn raw material were separated and recovered, the former being copper slag, and the latter being a zinc raw material for the ISP method (a zinc smelting method using a blast furnace). The quality was as available. Since the amount of Cu in ash II was relatively small, Cu was not separated and recovered as a Pb raw material and a Zn raw material. As a result, Pb
A high-purity fractionated product of 43.6% and Zn 63.8% as a Zn raw material was obtained.

The analytical values of the wastewater obtained by neutralizing the supernatant of the second fractionation / recovery tank are shown in Table 3 in comparison with wastewater regulation values based on the Water Pollution Control Law. All of the components are below the wastewater regulation value, indicating that there is no problem as wastewater.

For comparison, the analysis of the amount of heavy metal in the solution for dissolving heavy metal, the calculation of the amount of heavy metal precipitated in each separation and recovery tank, and the control of the amount of sodium sulfide or sodium hydrosulfide added were not performed. Table 2 shows the analysis values of the separated and recovered products when sodium sulfide or sodium hydrosulfide was added in excess in the separation and recovery tank. In both cases of Ash I and Ash II, the results were inferior to the results of Example 1 (Table 1), indicating that the purity of Cu, Pb, and Zn was low.

It should be noted that, at the stage of precipitation and separation of sulfide in the second fractionation and recovery tank, even if all heavy metals in the solution in this tank are recovered, sulfide that can be used as a nonferrous smelting raw material can be obtained. For example, it is sufficient to add a slightly excessive amount of sodium sulfide or sodium hydrogen sulfide, collectively precipitate and separate and collect the precipitate and the supernatant without separating the precipitate from the supernatant. In that case, as shown in FIG. 2, the second separation and collection tank can be made into one tank, and the continuous treatment can be sequentially performed from each of the first separation and collection tanks. However, since the amount of heavy metal present in the supernatant of each first separation / recovery tank is different, every time the treatment liquid in the second separation / recovery tank changes, the continuous addition amount of sodium sulfide or sodium hydrosulfide is switched and operated. It is good to make the control system such that

In the embodiment (FIG. 2), the heavy metal dissolving tank and the first separation / recovery tank are assembled in three lines, but one or more lines may be arranged in parallel depending on the processing scale.
In FIG. 2, the first and second separation / recovery tanks are separated into two types of sulfide groups. However, in the case of separating into three or more types of sulfide groups, the sulfide groups are connected in series according to the number of groups to be separated. And a separate collection tank. At that time, it is advisable to use a batch (batch) processing method for the separation / collection tanks at the preceding stage except for the final separation / collection tank. For example, when separating into three types of sulfide groups, as shown in FIG. 3, the first to third separation and collection tanks are connected in series, the first and second separation and collection tanks are batch-processed, and the third separation is performed. Only the recovery tank may be of a continuous processing type. According to the method shown in FIG. 3, it is possible to separate three types of heavy metals, but equipment costs and processing costs are higher than in the case of separating two types of heavy metals. Should.

Although a pH adjusting tank is provided in FIG. 2, a system without the pH adjusting tank as shown in FIG. 4 may be used. In this method, the pH can be released in the mixing tank before the second separation / recovery tank.
After that, if necessary, desalination treatment, and if not necessary, discharge. In the case of this method, it is considered that a new precipitate due to pH adjustment is mixed in the precipitate in the second fractionation recovery tank. As shown in Table 4, Cu,
It was found that the purity of Pb and Zn was not significantly different from the case where the treatment was performed by the method shown in FIG.

According to the system shown in FIG. 4, there is an advantage that the wastewater treatment process can be simplified. In addition, even when the pH is adjusted in a single process, even if the amount is small, it is necessary to treat the precipitate generated there. Since it is processed as a smelting raw material, there is an advantage that it can contribute to a reduction in the processing cost of the neutralized precipitate. However, this method should not be used when the sediment mixed during the neutralization treatment has a significant adverse effect on the quality of the non-ferrous smelting raw material. Consideration needed.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

[0030]

[Table 4]

[0031]

According to the method for separating and recovering heavy metals from incinerated ash according to the present invention, the types and amounts of heavy metals in the incinerated ash to be separated and recovered differ from day to day as in the case of wide-area treatment. However, it does not cause a decrease in the recovery rate of heavy metals for the purpose of separation, separation and recovery, a decrease in purity, and an increase in the content of sulfur components in the treated wastewater. As in the case where the types and amounts of heavy metals in incinerated ash are constant, heavy metals for the purpose of separation, separation and recovery can be separated and collected with high purity and a high recovery rate as sulfides, and sulfur components in treated wastewater can be contained. The amount can be reduced and the treated wastewater can be rendered harmless.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the pH of a solution and the concentration of lead in the solution.

FIG. 2 is a diagram illustrating a process flow for separating and recovering heavy metals from incineration ash according to an example.

FIG. 3 is a diagram illustrating an example of a process flow for separating and recovering heavy metals from incineration ash according to the present invention.

FIG. 4 is a diagram illustrating an example of a process flow for separating and recovering heavy metals from incineration ash according to the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C22B 15/00 102 C22B 3/00 Q 19/20 13/04 (72) Inventor Yoshifumi Kameoka 1-chome, Takatsukadai, Nishi-ku, Kobe-shi, Hyogo Prefecture. No. 5-5 Kobe Steel, Ltd.Kobe Research Institute (72) Inventor Hiroaki Kawabata 1-3-18, Wakihama-cho, Chuo-ku, Kobe-shi, Hyogo Kobe Steel, Ltd.Kobe Main Office (56) References Special 56-87634 (JP, A) JP-B 27-5003 (JP, B1) (58) Fields investigated (Int. Cl. ⁶ , DB name) C22B 7/02 B09B 3/00 B09B 3/00 ZAB C22B 3/44 C22B 13/00 C22B 15/00 102 C22B 19/20

Claims (6)

(57) [Claims] 1. A heavy metal dissolving step for dissolving heavy metals in incinerated ash in a heavy metal dissolving tank to obtain a heavy metal dissolving solution, feeding the solution to a first separation and recovery tank, and sulfurizing the solution in this tank. By supplying soda or sodium hydrosulfide and adjusting the pH of the solution, a first fractional recovery step of precipitating and separating a part of heavy metals in the solution as sulfide and separating the solution after the precipitate separation By feeding the solution to the second separation / recovery tank and supplying sodium sulfide or sodium hydrosulfide to the solution and adjusting the pH of the solution, some or all of the heavy metals in the solution are converted into sulfides. Second to precipitate and separate
A method for separating and recovering heavy metals from incinerated ash, comprising a step of separating and recovering heavy metals from the incinerated ash by quantitative analysis of the heavy metal content in the heavy metal dissolving solution for each type of heavy metal. Calculating the amount of heavy metal to be precipitated and the amount of heavy metal to be precipitated in the second separation and recovery step,
The amount of sodium sulfide or sodium hydrosulfide to be supplied in the first separation and recovery step is set as a sulfur amount, based on an amount chemically equivalent to the calculated amount of heavy metal precipitated in the first separation and recovery step, The amount of sodium sulfide or sodium hydrogen sulfide supplied in the second separation and recovery step is set as a sulfur amount on the basis of an amount chemically equivalent to the calculated amount of heavy metal precipitated in the second separation and recovery step. A method for separating and recovering heavy metals from incinerated ash. 2. In the second separation and recovery step, after a part of heavy metals in the solution is precipitated as sulfide and separated, the solution after the separation of the precipitate is fed to a third separation and recovery tank, where the solution is separated. By supplying sodium sulfide or sodium hydrosulfide to the solution and adjusting the pH of the solution, a third fractional recovery step of precipitating and separating some or all of the heavy metals in the solution as sulfides is provided, The amount of sodium sulfide or sodium hydrosulfide supplied in the third separation and recovery step is defined as the amount of sulfur and is based on an amount that is chemically equivalent to the amount of heavy metal precipitated in the third separation and recovery step calculated from the analytical value. 2. The method for separating and recovering heavy metals from incinerated ash according to claim 1, wherein: 3. The heavy metal from incinerated ash according to claim 1, wherein the pH of the solution is adjusted by adding an alkali or an acid to the solution, and the pH of the solution is confirmed by measuring the pH with a pH meter. Separation and collection method. 4. The incineration according to claim 1, wherein the heavy metal precipitated as sulfide in the first fractional recovery step is copper, and the heavy metal precipitated as sulfide in the second fractional recovery step is lead and zinc. Separation and recovery of heavy metals from ash. 5. The incinerated ash according to claim 1, wherein the heavy metal precipitated as sulfide in the first fractional recovery step is lead, and the heavy metal precipitated as sulfide in the second fractional recovery step is zinc. Heavy metal separation and collection method. 6. The heavy metal precipitated as sulfide in the first separation and recovery step is copper, the heavy metal precipitated as sulfide in the second separation and recovery step is lead, and the sulfide is precipitated in the third separation and recovery step. 4. The method according to claim 2, wherein the heavy metal precipitated as zinc is zinc.